LU-7329 obdclass: sync device to flush journal callbacks

LU-7329 obdclass: sync device to flush journal callbacks

After llog_test_10() has been added to check correct Catalog
wrap-around as part of LU-6556, frequent auto-tests failures
have been encountered due to OOM situation on VMs caused by
a lot of journal commit callbacks backlog induced by the huge
LLOG activity generated by new test.
This patch forces frequent device sync to flush these journal
commit callbacks.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: If06914a395f5bacbbb55fcdc229ffcd47d742843
Reviewed-on: http://review.whamcloud.com/17052
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>